Lighttpd

In the function {{{connection_handle_write_prepare()}}}, "lines 537ff. of connections.c":source:tags/lighttpd-1.4.15/src/connections.c@current#L537 (rev. 1716) are as follows:

/* disable keep-alive if size-info for the body is missing */
if ((con->parsed_response & HTTP_CONTENT_LENGTH) &&
    ((con->response.transfer_encoding & HTTP_TRANSFER_ENCODING_CHUNKED) == 0)) {
    con->keep_alive = 0;
}

Given the intention stated in the comment, it is likely that the condition in line 538 is reversed, and the whole should rather read:

if ((!(con->parsed_response & HTTP_CONTENT_LENGTH)) &&
    ((con->response.transfer_encoding & HTTP_TRANSFER_ENCODING_CHUNKED) == 0)) {
    con->keep_alive = 0;
}

Indeed, as {{{con->keep_alive}}} seems to be never set back to 1 anywhere in {{{connection_handle_write_prepare()}}} (or elsewhere down the execution flow), lighttpd returns a ''Connection: close_ header and resets the connection even when the client sends a _Connection: keep-alive'' request. Moreover, if an upstream handler (e.g. a process behind mod_fcgi) responds with a ''Connection: keep-alive'' header, the client gets the connection reset anyway.